The present invention relates to a color correction structure for a color imaging device for correcting color using a plurality of filters.
A color imaging device, such as, for example, a color copy machine and the like, is arranged such that the imaging light of a color document is projected to a color photoconductive material; the color photoconductive material is exposed by the image light of the document; and thereafter, the color photoconductive material is subjected to development and fixing processes to provide a copy of color. The exposure of the color photoconductive material is carried out by focusing the image of the color document on the surface of a photoconductive agent of the color photoconductive material by an optical system having a focusing lens.
This type of color imaging device is provided with a color correction structure so that the spectral distribution of an image light can be adjusted in correspondence with the spectral sensitivity characteristics of (i.e., the property of sensitivity which is different depending upon a wavelength) of a photoconductive material, so that the tone of a document can be corrected or the color of the document can be changed to an arbitrary color. Further, an amount of light adjustment structure is also needed.
The amount of light adjustment structure is, usually composed of a variable diaphragm that is disposed in a focusing lens.
The color correction structure is composed of a plurality of filters. These filters absorb 100% of a monochromatic light of a specific color, and are disposed midway in the light path of an image light, so that the amount of interference of the filters with the light path can be independently adjusted. These filters are usually composed of three kinds of filters, a yellow filter for absorbing a blue light, a magenta filter for absorbing a green light and a cyan filter for absorbing a red light, and they are used in combination.
The aforesaid color correction stucture is preferably incorporated in the focusing lens from the view point of the space efficiency of the imaging device as a whole.
Nevertheless, in this arrangement, both color correction structure and amount of light adjustment structure are incorporated in the focusing lens, and as a result, the focusing lens is increased in size thereby to increase the size of the imaging device as a whole. Further, the color correction structure and amount of light adjustment structure are made complex because a driving mechanism must be provided with each structure.
To cope with this problem, there is an arrangement for reducing the size of the interior of a focusing lens incorporating filters. According to this conventional arrangement, two slender filter plates, each having a filter region for absorbing a monochromatic light of different color, are disposed on opposite sides of a transparent transmitting filter region. The two filter plates are independently moved in a longitudinal direction thereof and disposed in a direction perpendicular to the light axis of the focusing lens so that the respective filter regions can interfere with the light path in the focusing lens.
For example, a first filter plate, including a yellow (hereinafter, abbreviated as Y) filter and magenta (hereinafter, abbreviated as M) filter disposed on the opposite sides of a transmitting region, and a second filter plate including a cyan (hereinafter, abbreviated as C) filter and yellow (Y) filter disposed on the opposite sides of the transmitting region are positioned in the focusing lens so that they can be independently moved in the longitudinal direction thereof. With this arrangement, the Y, M or C filter can be independently caused to interfere with the light path in such a manner that the transmitting region of one of the filter plates is located in the light path and the other filter plate is moved to cause an arbitrary filter to interfere with the light path. Further, the Y and M filters, the M and C filters, or the C and Y filters can be caused to interfere with the light path in combination by relatively moving both filter plates.
With this arrangement, the size of the filter portion can be reduced because the three filters can be replaced with the two filter plates.
Nevertheless, the two filter plates must be spaced apart from each other in the optical axial direction of the focusing lens because the two filter plates are moved relatively to each other. In this arrangement, a problem of the occurrence of an irregular color arises because these two filter plates interfere with the light path at different positions in the optical axis direction.
More specifically, when filters of the two filter plates correct color in combination, the two filters are dislocated in the optical axial direction. As a result, when lights are supplied from different points on the document in the width direction thereof which is parallel with the direction in which the filter plates are moved (the direction along which the filters enter a light path and exits therefrom), the ratios of the areas of the light paths formed by these lights and occupied by these two filters, respectively, to the entire areas thereof (amounts of interference of the filters with the light paths) are different, to thereby cause the irregular color.
This will be described more specifically with reference to the schematic diagram of FIG. 1, showing two different points A and B located in the width direction of the document 80. The filter 91A of a first filter plate 91 has an amount of interference with the light path formed by the image light from point A: LA1 and an amount of interference with the light path formed by the image light of the point B: LB1 which is different from LA1 (LA1.noteq.LB1). In the same way, filter 92A of a second filter plate 92 has an amount of interference with the light path formed by the image light from the point A: LA2 and an amount of interference with the light path formed by the image light of the point B: LB2 which is different from LA2. As a result, the amount of color correction at point A is different from that at point B.
Further, since the filters are located in the focusing lens, when they are not flat and not parallel with each other, the optical performance of the focusing lens is greatly degraded by the optical action of the filters. Consequently, a problem arises in that the filters must be formed with a pinpoint accuracy, and thus become expensive.